Piston for internal combustion engine



Oct. 13, 1931. c. BORGO ET AL PISTON FOR INTERNAL COMBUSTION ENGINES Filed Dec. 1, 1930 nual veN T425 f. Rosagga WW/t4 Patented Oct. 13, 1931 PATENT OFFICE CAB-LO BORGO AND ELISIO ROSAZZA MANUEL, OF T'UBIN, ITALY PISTON FOR INTERNAL COMBUSTION ENGINE Application filed December 1, 1930, Serial No. 499,348, and in Italy December 20, 1929.

It is known in connection with pistons, and

particularly hollow pistons made of cast aluminum employed in internal combustion engines, that there is always the latent danger 6 that seizing will occur at the two zones below the supports of the connecting gudgeon pin at the head of the connecting rod. This danger is very probably due to the unsymmetrical deformations of the piston at these zones during the operation of the engine and due to causes of both mechanical and thermal origin. The diameter of the piston in the direction of the gudgeon pin, tends to increase either by reason of the. forces exerted in an alternating manner on the supports of the gudgeon pin, or by. reason of the greater thermal expansion in this direction caused by the greater concentration of metal due to the presence of the said supports.

To obviate this danger it has previously been proposed to provide cavities in these danger zones of the piston, during or after the casting process. But the object is not attained in this manner for if the danger of seizing is-eliminated at the point where, by reason of the cavities there is no longer contact between the piston and the cylinder, this danger still exists along the lines of connection between the cavities and the remainpiston.

Furthermore along these connecting lines this danger is increased owing to the greater pressure per unit area existing there.

It has also been proposed to provide at the periphery of the cylindrical wall of the piston, and normally to its generating lines, a number of parallel grooves traversing the two danger zones of the piston itself. This arrangement is satisfactory as regards obviating seizing, but it ossesses another somewhat serious defect, t 's defect being that the said grooves also extend over the sides of the piston wall, that is to say on the effective surfaces supporting the piston against the wall of the cylinder. The effective area of these supportlng surfaces .is therefore reduced,

Y which increases the pressure per unit area and consequently the wear. 4 Now the present invention, with the object ing portion of the cylindrical wall of the,

of obviating the danger of seizing and at the same time avoiding the defects resented by the previous propositions, has or its object an arrangement in which the danger zones of the cylindrical wall of the piston below the supports for the gudgeon pin, are provided with a number of parallel grooves normal to the generating lines of the said cylindrical wall and restricted solely to the zones liable to seize referred to above.

These grooves have a maximum depth and width at the centre of the danger zones and diminish both in depth and in width, on each side of the said central part until they vanish at the boundary between the said zones and 66 the intermediate zones supporting the piston against the cylinder wall.

A constructional form of the improved piston according to the present invention is shown, merely by way of example, in the 'ac- 70 companying drawings, in which :Figure 1 illustrates the piston in front elevation, that is to say with the axis of the supports for the gudgeon pin normal to the plane of the drawing; Figure 2 is a partial side elevation of the piston; Figure 3 is a horizontal section of the piston, on the line 3w-3a: of'Figure 1 on a larger scale; Figure 4 illustrates in elevation, also on a larger scale, a portion of the piston.

The piston itself may be of any known type and form, having in its interior t wo substantial sockets 1, constituting the supports in which the gudgeon pin connecting the head of the connecting rod with the piston is 85 mounted, these sockets beingconnected to the 'cylindrical wall 2 of the piston, to which they may be secured also by means of internal strengthening ribs 3. i

According to the present invention, above the two zones a of the cylindrical wall of the piston which are below the supports 1 for the gudgeon pin, a number of parallel grooves 4, normal to the generating lines of the said 0 lindrical wall of the piston, is provided, e series of these grooves starts directly below the oil-scraper segment intended to be located in the lowermost ring groove 5 of the piston or else below the oilcollecting groove 6 itself, and extends downwards to the lowest point of the supports 1. These grooves, which are preferably of triangular section (see Figures 2 and 4) have their maximum width and depth at the centre 5 of each zone --a-, whilst they extend on both sides of this centre part, diminishing gradually both inwidth and depth until they vanish at the limit between the two zones aand the two zones b which are at right angle in respect to those -w, and according to which the effective support of the piston occurs on the wall of the cylinder durmg operation. These zones b are not provided with grooves and their whole surface is utilized effectively with the'object of the said support a ainst' the wall of the cylinder. Oh the ot or hand the presence of the grooves 4 in the danger zones a practically excludes any fear of seizing.

As already stated, the cross-section of the grooves 4 is preferably of triangular form, but any other section may be adopted.

It is moreover evident that the present invention is in no way limited to the particular arrangements described and illustrated, but that, without exceeding the scope of the'invention it may be subjected to any alterations that the circumstances or requirements of practice may render necessary or advisable.

We claim:

A piston for internal combustion engines, particularly of the hollow cast aluminum type, in which a number of grooves are provided on the cylindrical wall of the piston,

these grooves being limited to the two zones below the supports for the connecting gudgeon pin at the head of the connecting rod, and being substantially normal to the generating lines of the said cylindrical wall,

40 and presenting a maximum depth and width in line with the middle art of said zones and diminishin to zero both in depth and width at each slde of this middle part until they vanish at the boundary between the said zones and intermediate zones for supporting thepistomagainst the cylinder walls, with the obJect of preventing all danger of seizing of the piston" at the said zones.

- In testimony whereof we have afiixed our signatures. p

CARLO BORGO.

ELISIO ROSAZZA MANUEL. 

